In a multitude of commercial applications, it is common to employ a heavy duty conveyor belt for the purpose of transporting product and material. The belts so employed may be relatively long, on the order of miles, and represent a high cost component of an industrial material handling operation. In many applications, the belts are susceptible to damage from the material transported thereby, and a rip (slit, cut or tear) may develop within the belt. A torn or ripped belt can be repaired once detected. The cost of repairing a heavy duty conveyor belt and the cost of cleaning up material spilled from the damaged belt can be substantial. If, however, such a rip or tear commences and the belt is not immediately stopped, the rip can propagate for a substantial distance along the belt. It is, therefore, desirable to detect and locate a rip in the belt as quickly as possible after it commences and to immediately terminate belt operation, whereby minimizing the extent of the damage to the belt.
It is well known to employ sensors within conveyor belts as part of a rip detection system. In a typical system, sensors in the form of loops of conductive wire are affixed or embedded in the belt and provide a rip detection utility as part of an overall rip detection system. Rip detection is achieved through the inferential detection of an “open circuit” condition in one or more of the sensor loops in the belt. Typically, an electrical energy source external to the belt is inductively coupled to a sensor loop in the belt. A break in the conductive wire loop of the sensor may be detected by a remote transmitter/receiver (exciter/detector). Disposition of a plurality of such sensors at intervals along the conveyor may be effected with each sensor passing within read range of one or more exciter/detectors at various locations. A rip or tear will encounter and damage a proximal sensor loop and the existence of the tear will be detected when the proximal sensor loop damage is detected as an open circuit by the reader at its next pass. In this manner, the existence of a tear will be promptly detected and repaired and damage to the belt is minimized.
While existing rip detection systems are known to operate reliably and well, there is a continuing effort to improve system performance. In that regard, several areas for potential improvement have been identified. First, in some operational environments, the electrical noise is so great that a poor signal-to-noise ratio significantly decreases the accuracy of the rip detector function. Moreover, it has been observed that with a conveyor belt carrying antennas intended for inductive coupling, much of the electrical noise introduced to the receiver is derived from capacitive cross-coupling. This is primarily of a capacitive nature, between the probes of the transmitter and receiver via the belt itself and/or apparatus associated therewith, such as the rollers, drive wheels, support frame, etc. The magnitude of the electrical noise signal in a conveyor belt rip detector often approaches the magnitude of the transmitter signal; and, therefore, it is quite difficult to sense a received transmitter signal with accuracy, especially in particularly electrically noisy environments in which conveyor belt rip detectors often are found.
Second, wear, stretching, contraction, dirt, other environmental conditions, etc. may cause a variation in the efficiency of signal coupling, whether of the capacitive, inductive, optical, or any other type of coupling, between the sensor loops (or other signal coupling means carried by the belt) and the transmitter and the receiver at a rip detector station. Such efficiency variation will vary the magnitude or other parameter of the input signal delivered from the receiver to the detector, which may detrimentally affect operation of the entire system. Hence, there is a need for a sensor loop detection system that is less sensitive to other environmental conditions as well as the distance between the detector and the conveyor belt.
Third, by monitoring the magnitude and phase of a signal received from a detected loop, a sensor loop detection system can be utilized to detect either inverted or noninverted sensor loop configurations. In some applications, a section of conveyor belt having one sensor loop configuration, for example, an inverted or figure eight configuration, is spliced with a section of conveyor belt having another configuration, for example, a noninverted loop configuration. In such an application, it is necessary that the sensor loop detection system be able to operate effectively with both sensor loop configurations simultaneously.
Fourth, many known systems use inductive coupling to excite the conductive sensor loops in the belt; and known automatic gain control circuits utilize a relatively large capacitance. Such a large capacitance requires electrical shielding and filtering and hence, is relatively costly. Thus, there is a need to develop a sensor drive system that does not require such a large capacitance and its associated electrical shielding and filtering.